1. Field of the Invention
The present invention relates to systems that determine optical loss characteristics of optical fibers. More particularly, the present invention relates to systems and methods used to determine the optical loss characteristics of a particular optical fiber pathway in an optical fiber network by testing at only one point on the optical fiber pathway.
2. Description of the Prior Art
There are many applications that utilize an optical fiber network to establish optical communications between a host digital terminal (HDT) at a central office and an optical network unit (ONU) at a remote location. Since a central office serves as the point of origin for the optical fibers in the optical fiber network, equipment is used at the central office to organize the various optical fibers in the optical fiber network. In certain optical networks, the optical fibers at the central office are connected to dedicated pieces of equipment, such as optical signal transmitters, that serve only one purpose. If the optical fibers are to be connected to another piece of equipment, such as test equipment, the optical fibers must be manually connected to that new piece of equipment.
In more versatile applications, optical fibers are terminated at fiber administration systems at the central office. Fiber administration systems enable many different types of equipment to be connected to the optical fibers without having to reroute the optical fibers from their point of termination. Such fiber administration systems are exemplified by the LGX(copyright) fiber administration system which is currently manufactured by Lucent Technologies of Murray Hill, N.J., the assignee herein.
After optical fibers have been routed between the central office and the telecommunications provider and various ONUs, the optical fiber must be tested. Among the tests performed on newly laid optical cables is an optical loss test. For this test, a calibrated light source is used to transmit light signals through the optical fibers. The calibrated light source typically transmits test signals at the same frequencies that will be used in the optical fibers being tested. The calibrated light source is then measured at the far end of the optical fiber. After comparing the transmission signal to the received signal, the loss characteristics of each optical fiber can be quantified.
Typically, the testing for determining the loss characteristics of a particular optical pathway are done in two directions. In the first direction, loss testing is done from the telecommunication provider""s facility to an ONU. In the second direction, the same optical fibers are tested from the ONU back to the telecommunication provider""s facility. Each optical fiber exhibits different loss characteristics depending upon the direction of the signal transmission.
In order to perform loss characteristic testing, a technician is typically sent to the customer facility with a calibrated light source and signal monitoring equipment. A second technician with the same equipment remains at the telecommunication provider""s facility. The two technicians then coordinate testing to obtain the loss characteristics of the optical fibers in both directions. Every time the optical cable is altered between the customer facility and the telecommunications facility, loss testing may again have to be initiated.
Calibrated light sources are extremely expensive. Furthermore, the use of two technicians to quantify a pair of optical fibers is a highly labor intensive and expensive procedure. Consequently, the prior art method of testing optical fibers requires a large commitment of time, labor and equipment. A need therefore exists for a system and method that can be used to determine loss characteristics of optical fibers without the need of a dedicated calibrated light source and without having to send a technician to a remote location.
The present invention is a system and method for determining the optical loss characteristics of optical fibers in an optical fiber network. An optical transmission module is provided. The optical transmission module produces a light signal and an electrical signal that contains data regarding the characteristics of the light signal being generated. The light signal output of the optical transmitter module is connected to the input of a calibrated optical switch. The outputs of the optical switch are connected to the optical fibers that are to be tested.
At the opposite ends of the optical fibers, a second optical switch is provided. The second optical switch connects the various optical fibers to a monitor module. The monitor module detects the light signal transmitted by the optical transmitter module through the various optical fibers. The monitor module converts the received light signal into a corresponding electrical signal.
A systems controller is coupled to both the optical transmitter module and the monitor module. Knowing the optical losses caused by the optical switches, the systems controller can compare data about the light signal from between the optical transmitter module and the monitor module, thereby determining the loss characteristics of the optical fibers between the optical transmitter module and the monitor module.
Depending upon the configuration of the optical fiber network, the optical transmitter module and the monitor module can be located either at the same facility or at remote facilities.